Disc drives are the primary devices employed for mass storage of computer programs and data used in computer systems. Contemporary disc drives use rigid discs, which are coated with a magnetizable medium for storage of digital information in a plurality of circular, concentric data tracks. The discs are mounted on a spindle motor, which causes the discs to spin and the surfaces of the discs to pass under respective bearing disc head sliders. The sliders carry transducers, which write information to and read information from the disc surfaces. The combination of the slider and the read/write transducer is also known as a read/write head (hereinafter “head”). An actuator mechanism moves the heads from track-to-track across the surfaces of the discs under control of electronic circuitry. The actuator mechanism includes track accessing arms and suspensions for supporting the heads.
Head suspensions typically include a load beam, a gimbal that supports the head, and a flex circuit providing an electrical connection to the read/write transducer of the head. The gimbal is typically an etched gimbal ring that is welded to the load beam. The flex circuit is generally routed over or adjacent to the gimbal and the head. During operation, the load beam applies a downwardly directed load force to the head at a load point. As the disc rotates, air is dragged and compressed under bearing surfaces of the head creating a hydrodynamic lifting force that counteracts the load force and causes the head to lift and fly on an air bearing in close proximity to the disc surface. The gimbal includes flexure features that allow the head to pitch and roll over the load point while following the topography of the disc. The air bearing maintains spacing between the transducer and the disc surface, which reduces transducer efficiency. However, the avoidance of direct contact with the disc surface vastly improves the reliability and useful life of the head and disc components.
The disc drive industry has been progressively decreasing the size and mass of the slider structures in order to reduce the moving mass of the actuator assembly and to permit closer operation of the transducer to the disc surface. The former giving rise to faster data access and the latter giving rise to improved transducer efficiency that can be traded for higher data storage capacity. The size (and mass) of a slider is usually characterized with reference to a so-called standard 100% slider, known as a mini-slider. The term 70%, 50% and 30% slider are respectively known as a micro-slider, a nano-slider, and a pico slider, which are more recent low mass sliders that have linear dimensions that are scaled by the applicable percentage relative to the linear dimensions of a standard mini-slider.
Although smaller, low mass heads can provide both performance and economic advantages, the reductions in physical slider dimensions give rise to numerous problems that do not necessarily scale linearly with the dimensional changes. If, for example, the size and load force on the slider was simply halved, the air bearing stiffness in the pitch direction will be reduced on the order of one-eighth. Accordingly, the flexure features of the gimbal must have sufficient compliance to allow the slider adequate freedom to pitch and roll in order to maintain the trailing edge of the slider where the transducer is located at the desired distance from the rotating disc surface. Failure to do so, can lead to signal modulation, data loss, or even catastrophic failure of the head or disc components. Accordingly, suspensions designed for use with pico-sliders must include gimbals having highly compliant flexure features.
The conventional steel gimbal described above is generally too stiff to provide the desired compliance for operation with pico sliders. Gimbals having highly compliant flexure features are being developed. Unfortunately, such highly compliant gimbals and the heads they support become more susceptible to damage caused by large vertical displacement in response to a shock event.
Shock events can occur due to forces applied during assembly, fly testing, shipping, and handling of the suspension, or during use of the disc drive. For example, a transportation shock may generate displacement forces large enough to cause the delicate flexure features of the gimbal to bend past their yield point, which may result in a separation between the load beam and the head at the load point. Also, certain disc drives have a ramp which lifts the load beam to unload the slider from the disc surface during start and stop of disc rotation. If the slider is a self-loading slider, sub-ambient pressure developed between the slider and the disc surface can cause a large vertical displacement of the gimbal as the slider is lifted from the disc surface. Additionally, shock events that occur while the suspension is supported by the ramp, can also cause potentially damaging displacement of the head relative to the load beam.
Embodiments of the present invention provide solutions to these and other problems, and offer other advantages over the prior art.